In the field of computing, there has been an ever-increasing need for greater and more rapid data processing. To satisfy these needs, there have been many significant advances with respect to the design of faster and more complex processors, application specific integrated circuits (ASICs), and the like. Such complex circuits sometimes take advantage of the use of multiple parallel processors and ancillary circuitry.
Increased processing speeds are often accompanied with the need to increase the speed of communication across signaling paths between a processor and other processors or other ancillary circuitry. At higher communication speeds, however, transmission line effects of the signaling paths become more significant. These transmission line effects, such as signaling delay, may be reduced by shortening the length of the signaling paths.
Furthermore, as the clock frequency of electronics increases, the physical distance between components on a data path becomes more and more critical. This physical distance is particularly important between an integrated circuit such as an ASIC and a memory module such as a cache that is connected to the integrated circuit. The physical distance between such components will impact the access time and, therefore, the performance of the resulting circuit assembly.
One method of reducing the physical distance between circuit components is to stack the circuit board onto which they are assembled. For example, the signaling path between a first component on a first circuit board and a second component on a second circuit board may be reduced by stacking the first and second circuit boards. In addition to shortening signaling paths, stacking of circuit boards permits manufacturers to partition circuit modules on individual circuit boards; to manufacture smaller, less expensive circuit modules; to improve configurability and upgradability; and to achieve other benefits of such construction.
When circuit boards are stacked, however, air flow may be restricted such that it becomes difficult to adequately cool the circuit components on the circuit boards. If cooling capability is not improved, higher operating temperatures may result in premature failure of circuit components. A possible alternative, redirecting air flow, may be impossible due to other design constraints or may be too costly.
Attempts have been made to improve heat dissipation from a circuit board. For example, U.S. Pat. No. 5,014,904 to Morton describes a method and apparatus for dissipating heat from printed circuit boards and electronic devices mounted thereon. The printed circuit boards are provided with apertures for receiving thermal conductor pads. One end of each thermal conductor pad is secured to the bottom of an electronic device which is mounted on one side of a printed circuit board. The opposite end of the thermal conductor pad contacts a cold plate which is mounted on the opposite side of the printed circuit board.
U.S. Pat. No. 4,628,407 to August et al. describes a circuit module including electronic devices mounted on a circuit board. The circuit board includes conductive pads and plated-through holes forming a conductive flow path from each electronic device to the opposite side of the circuit board. The heat pads and plated-through holes can be connected with the circuit board's ground layer for better heat distribution.
Nevertheless, there is a need to improve the cooling of circuit boards that are stacked with respect to one another. Accordingly, it is an object of this invention to provide an improved stacked circuit board assembly that is adapted for improved heat dissipation.